There are a variety of keyword retrieval systems known in the art, but they generally do not take into account the special needs of a student working on a computer-assisted instruction system. Such a student is often unfamiliar with the instruction system, and also unfamiliar with the subject matter of the course in which the student happens to be engaged. Some examples of retrieval schemes in the literature are indicated below.
A Bharwani et al. U.S. Pat. No. 3,670,310 teaches a storage and retrieval system employing link addresses for tracing a search path through plural files. Retrieval is based on the use of keywords provided by a user and, by that user, joined by connectors. The retrieval of specific information is based upon the frequency of occurrence of the input keyword that happens to be found in the target database.
A U.S. Pat. No. 4,255,796 to Gabbe et al. shows an associative searching arrangement which uses query masks and requires user feedback from time to time during the course of a search in order to narrow the focus of the search.
A Millett et al. U.S. Pat. No. 4,318,184 shows an information storage and retrieval system and method in which the entry of keywords causes nodes, or paths, in a hierarchical information tree structure to be identified by binary bitstrings that can be logically combined to define a set of paths. Those paths may then be traced for accessing all data in the database corresponding to the input keywords.
Glickman et al., in the U.S. Pat. No. 4,358,824, show a retrieval system which interprets a user's free-form query; and, in doing so, the system employs a parts-of-speed directory to select items from a document. The relative importance of keywords is weighed, and the documents with the largest retrieval values are selected for retrieval.